POTASSIUM IN PLANT GROWTH AND YIELD by Ismail Cakmak Sabanci University Istanbul, Turkey

1. POTASSIUM IN PLANT GROWTH AND YIELD by Ismail Cakmak Sabanci University Istanbul, Turkey

2. LowK High K High K LowK High K LowK LowK High K

3. Control K Deficiency Cakmak et al., 1994, J. Experimental Bot.

4. POTASSIUM IN CROP PRODUCTION Alleviation of Effects of Stress Factors Water Regime Photosynthesis K Protein Synthesis Enzyme Activation Cell elongation Phloem Export of Photosynthates

5. K and Cell Elongation/Extension In most cases, cell extension is the consequence of the accumulation of K in the cells that is required for both stabilizing the pH of the cytoplasm and increasing the osmotic potential in vacuoles. Cell elongation by GA is dependent on K supply

6. Potassium is essentially needed for cell elongation Potassium is essential for GA3 (gibberellin)-induced cell elongation/extension, especially under deep-seeding conditions (seedling establishment!!!) Potassium is needed for turgor potential to avoid drought stress in arid environment Potassium and GA act synergistically in elongating cells (Chen et al., 2001; Plant Cell Environ. 24: 469-476)

7. Rogg et al., 2001, Plant Cell Auxin-stimulated cell elongation is also dependent on presence of potassium. There is a strong correlation between expression of K-channel proteins and cell elongation following application of auxin Auxine defective line

8. TRH1 encoding a potassium transporter protein: essential for root tip growth. As cell elongation is driven by turgor pressure, the operation of K translocators is crucial for growth. In the mutant lines without TRH1 protein root hair formation was totally blocked.

9. Line with TRH1 Line without TRH1 Root Hair Formation With K protein Without K protein Rigas et al., 2001, Plant Cell, 13: 139-151

10. TRH mediating K transport essential for root hair formation trh1 +TRH1 Wild Type trh1 Mutant Scanning electron micrographs Rigas et al., 2001, Plant Cell, 13: 139-151

11. Potassium is a critical mineral nutrient in tree growth and wood formation. In cambial region and xylem differention zone a strong potassium demand has been shown. Differentiating xylem cells involved in wood formation represent a strong sink for potassium that provides the driving force for cell expansion Langer et al., 2002; Plant Journal, 32: 997-1009

12. K nutritional status strongly affects development of wood producing cells Potassium concentration in xylem tissue, cambium/xylem differention zone and phloem tissue cambium/xylem xylem phloem Langer et al., 2002; Plant Journal, 32: 997-1009

13. Under K deficiency cambial and cell-expansion zones lack 2-3 cell layers each adequate K low K Cambium Cambium Xylem expansion zone Xylem expansion zone 0.05 mM K 10.0 mM K Langer et al., 2002; Plant Journal, 32: 997-1009 Lack of cell divisions in the vessel development region results in reduced wood production

14. The cambium cells divide and make new wood on the inside and new inner bark on the outside. In this way, a tree gets bigger around as it grows!

15. Potassium is highly needed for woodproduction. Potassium is driving force for expansion of wood producing cells

16. Photosynthesis and Potassium • In K-deficient leaves photosynthesis is • impaired at different levels • stomatal CO2 flux into chloroplasts • conversion of light energy into chemical energy • rubisco activity/CO2 reduction • phloem export of photosynthates and, • detoxification of toxic O2 species

17. Photosynthesis and Potassium During a mild K deficiency in cotton, increased stomatal resistance is first to result in a decrease in net photosynthesis and, as the deficiency becomes more acute, biochemical factors contribute. K K K Day 13 Day 19 Day 26 +K +K -K -K Severity of K deficiency Bednarz, et al. 1998, Environ. Exp. Bot. 39: 131-139

18. Effect of Varied K Supply on Photosynthesis in Cotton adequate K Photosynthesis Rate (µmol m-2 s-1) K deficiency Days Bednarz and Oosterhuis, 1999 ; J. Plant Nutr.

19. Decrease in photosynthesis with K deficiency becomes more distinct when plants are exposed to elevated CO2 concentrations • Enhanced K requirement of plants • when exposed toincreasing CO2concentration • in atmosphere

20. Effect of Elevated CO2 on Photosynthesis at Varied K Supply Adequate K 3.0 Low K high CO2 2.0 +K Assimilation Rate [µmol CO2 m-2 s-1] normal CO2 1.0 +K -K -K 0.0 Barnes et al., 1995, Plant Cell Environ.

21. Stomata regulating transpiration and CO2 uptake .K The transport of K+ across the plasma membrane and tonoplast causes the turgor changes of guard cells. Stomata open when guard cells accumulate potassium (red dots), which lowers the cells’ water potential and causes them to take up water by osmosis. The cells become turgid.

22. Role potassium in stomatal action When stomata opened, the K content of guard cells increased by factor 2, indicating a very rapid stomatal opening by K uptake opened closed Langer et al., 2004; Plant Journal, 37: 828-838

23. PHLOEM TRANSPORT K plays a critical role in phloem transport Source K Sink

25. Potassium is essential for transport of photosynthates into growing organs AKT2/3: a potassium channel protein and identified as photosynthate-induced phloem K channel. Flower induction and rosette development of the Arabidopsis with loss of AKT2/3 function (akt2/3-1 mutant) is delayed WT-AKT2/3 akt2/3-1 mutant Deeken et al., 2002, Planta, 216: 334-344

26. Accumulation of Phosynthates in K-Deficient Source Leaves Control K Deficiency Sucrose concentration (mg Glucose equiv. g-1 DW) 12 76 Cakmak et al., 1994b, J. Experimental Bot.

27. Decrease in Phloem Export of Sucrose by K-Deficiency Control K Deficiency Phloem Export of Sucrose (mg Glucose equiv. g-1 DW 8 h-1) 3.4 1.6 Cakmak et al., 1994b, J. Experimental Bot.

28. Relative distribution of total carbohydrates between shoot and roots (%) 84 97 Control K Deficiency 16 3 Cakmak et al., 1994a, J. Experimental Bot.

29. Plants suffering from environmental stress factors such as drought, high light intensity and salinity have larger requirement for potassium

30. Potassium Improved Photosynthesis Under Drought Stress Low K Adequate K Photosynthesis (µmol CO2 m-2 s-1) Drought Stress Sen Gupta et al., 1988, Plant Physiol.

31. Alleviation of Salt Stress by K Supply Membrane Damage (%) Chlorophyll (g kg-1 FW) NaCl + K supply NaCl Control Kaya et al., 2001, J. Plant Nutr.

32. Increased salt sensitivity in the absence of K transporter protein. AtHKT1 controls root/shoot Na+ distribution and counteracts salt stress in leaves by reducing leaf Na+ accumulation. Maser et al., 2002; FEBS Letters;531: 157-161

33. Growth of bean plants with low K supply under low and high light intensity Low light High light

34. SHADED PART Plants grown under high light intensity require more K than plants grown under low light

35. Enhancement of leaf symptomsof K-deficienyby high light NON-SHADED SHADED Partially shaded K-deficient bean leaves

36. REMEMBER:

38. Potassium deficiency makes plants sensitive to environmental stress factors. • Plants under environmental stress factors need additional potassium

39. FREE RADICAL DAMAGE TO CRITICAL CELL CONSTITUENTS O2 h.v. e- 1O2 O2._ H2O2 OH. DNA MEMBRANE CHLOROPHYLL PROTEIN S-H S-H S=S S=S LIPID PEROXIDATION MUTATION CHLOROSIS PROTEIN DAMAGE CELL DEATH

40. Conclusions • Potassium has several critical roles in plant growth and yield formation including cell elongation, maintenance of turgor pressure and photosynthesis, stomatal closure, protein synthesis and photoassimilate transport. • Potassium transporter proteins play critical role in K uptake and translocation (contributing to cell elongation) and tolerance to Na toxicity

41. Plants exposed to high light intensity or grown under long-term sunlight conditions like in southern countries in Northern Hemisphere have much larger K requirement • Improving K nutritional status of plants is a major contributing factor to the protection of plants from environmental stress factors under marginal conditions

42. Remark:During the late growth stage (generative phase) plants can need higher amount of potassium because at this stage • high amount of K is required for translocation of carbohydrates • plants can be exposed to more light and • topsoil with high root density and high K concentration can be dry (limited K uptake !) High need for late K application to foliar !!

43. Obrigado...